1. Field of the Invention
The present invention relates to a method for fabricating a vertical offset structure, and more particularly to a method for fabricating a vertical offset structure by extending specified trenches using a single wafer.
2. Description of the Related Art
A vertical offset structure is fabricated using a MEMS (Micro Electro Mechanical System) fabrication method. The MEMS fabrication method relates to fabricating systems of the micrometer dimension on a wafer (i.e., substrate) using a silicon process, and is based on the method of fabricating semiconductor devices. Representative systems which are fabricated using the MEMS fabrication method are accelerometers for measuring acceleration of moving objects, gyroscopes for measuring angular velocity of rotating objects, optical switches capable of controlling optical paths, etc.
The performance indicator of the vertical offset structure is determined depending on whether upper and lower electrodes of the structure have a complete vertical offset and how narrow the vertical gap between the vertical offset structures is in order to improve the performance of vertical driving and detection.
FIG. 1 is a cross-sectional view illustrating an example of a conventional vertical offset structure. This vertical offset structure is disclosed in U.S. patent application Publication No. 2002/0158293A1. The vertical offset structure, in which structure members having different thickness have a vertical offset, has a good performance in applications of vertical driving and detection. However, according to the vertical offset structure as illustrated in FIG. 1, the vertical offset is not produced on an upper electrode of the structure, but is produced on a lower electrode thereof. Thus, the vertical offset structure as illustrated in FIG. 1 has a degraded performance in applications using vertical driving and detection.
FIG. 2 is a view illustrating another example of a conventional vertical offset structure. This vertical offset structure is disclosed in U.S. Pat. No. 6,694,504 B2. According to the vertical offset structure as illustrated in FIG. 2, a complete vertical offset is produced on both upper and lower electrodes. However, according to the principle of the fabrication process, the horizontal gap gh between the upper and lower electrodes of the structure is limited to about 4.5 μm. Since the horizontal gap is limited, the improvement of performance of the vertical offset structure is limited.